As is known, automated manual transmissions have shift and select actuators, which may be controlled by a control device for carrying out gear ratio changes. In order to be able to control such gear shifting and selection processes as fast as possible and comfortably for the vehicle passengers, the control device requires exact information about the speed of the transmission input shaft and transmission output shaft. This particularly applies to unsynchronized automated transmissions provided with jaw clutches, in which the speed of the transmission input shaft has to be increased to a predetermined target speed by acting on the drive motor of the vehicle for carrying out a downshift, and in which the transmission input shaft has to be decelerated to a predetermined target speed by means of the transmission brake in case of an upshift. The respective target speeds in this case depend on the current vehicle speed and on the new gear ratio shift. These speed adjustments are made over a period in which a clutch between the drive motor of the vehicle and the transmission is disengaged and the current gear, as well as the new gear, has still not been engaged, the transmission being in its neutral position.
The above mentioned speeds are usually detected by means of speed sensors. Speed sensors of this type require a respective installation space in the area of the transmission input shaft and/or of the transmission output shaft in the narrow transmission housing. Besides, the installation in the transmission increases the manufacturing costs. Furthermore, it is desirable that in transmissions with a speed sensor at the transmission output shaft their speed values may be checked with regard to their plausibility in order to eliminate erroneous values from the transmission control.